Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.713488
Title: Microstructural evolution and mechanical properties of deeply undercooled eutectic alloys
Author: Clopet, Caroline Roberta
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2016
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Abstract:
An experimental investigation has been undertaken in an attempt to determine the mechanism of formation of anomalous eutectics. A melt fluxing method and a drop tube technique have been used to undercool eutectic Ag-Cu alloy. During the fluxing experiments, the growth fronts of the undercooled alloy samples have been monitored using high speed camera imaging. The evolved microstructures of the fluxed samples undercooled ≤ 60 K exhibit a trizonal structure consisting of mixed anomalous and lamellar eutectic. The high speed camera imaging reveals that the growth front propagates in a spasmodic manner, where periods of rapid growth are separated by significant intervals in which growth totally arrests. Depending upon undercooling, growth is either continuous or spasmodic. Continuous growth is characteristic of the advancement of a planar front, while during spasmodic growth a double recalescence occurs, the first of which is characteristic of the propagation of a dendritic front. The microstructure of drop tube processed Ag-Cu samples comprises of a mixture of lamellar and anomalous eutectic structures and a silver-rich phase, which appears as spherical inclusions at the eutectic cell boundaries. It is concluded that, during spasmodic growth, the propagation of eutectic dendrites is observed, which subsequently remelt to form the anomalous eutectic, while the lamellar eutectic grows during post-recalescence cooling. It is also postulated that this eutectic dendrite may be growing away from the eutectic point at high growth rates, which could lead to silver building up ahead of the interface that, in the drop tube samples, leads to the formation of the silver-rich phase observed at the cell boundaries. In the fluxed samples, as the silver builds up, the dendrite is no longer viable and growth arrests until sufficient silver atoms have diffused into the bulk liquid for the transient growth cycle to restart.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.713488  DOI: Not available
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